Lord Thaddeus survived the war and in 133 AC he was given the seat of the deceased Lord Roland Westerling in the council of seven that ruled as regents for the child king Aegon III Targaryen. After Lord Unwin Peake resigned as Hand of the King in 134 AC, Thaddeus was named to the position. With the return of the king's brother, Prince Viserys Targaryen, and his wife, Larra Rogare, whose brothers accompanied her to King's Landing, the ambitious Rogare family soon became embroiled in the conflicts of the regency of Aegon III. There were those at court who mistrusted the Rogares, with accusations of wrongdoing being spread back and forth by many parties. Lord Thaddeus, accused of treason and being involved in a plot with the Rogare family, was tortured for information and stripped of his position of Hand.

Thaddeus remained in his post as a regent until the council was dissolved in 136 AC.[3]